Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session R14: Waves: Surface Gravity Waves and Shear Currents |
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Chair: Miguel Bustamante, University College Dublin Room: C125-126 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R14.00001: Precession resonance mechanism in deep-water gravity surface waves Miguel Bustamante, Dan Lucas Discovered by Bustamante \emph{et al.} in 2014 and published in \emph{Phys. Rev. Lett.} in the same year\footnote{M.D.Bustamante, B. Quinn and D. Lucas, \emph{Phys. Rev. Lett.} \textbf{113}, 084502 (2014)}, \textbf{precession resonance} is a mechanism whereby strong nonlinear energy transfers occur between modes of oscillations whose frequencies are detuned: the amplitude-dependent precession frequencies of the phases help restore the resonance, hence the name ``precession resonance''. After explaining how this mechanism works and how robust it is, we will discuss new applications of this effect in systems of technological interest, focusing on deep-water gravity surface waves. We report transfer efficiencies of up to 40\%, depending on the numerical-experimental setup. All evidence gathered so far points to the conclusion that, to leading order, this effect is dominated by triad interactions at small (but finite) amplitudes. Joint work with Dan Lucas (DAMTP, Cambridge). [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R14.00002: On the interaction of gravity-capillary lumps in deep water Naeem Masnadi, James Duncan The nonlinear response of a water surface to a pressure source moving at a speed just below the minimum phase speed of linear gravity-capillary waves in deep water ($c_{min} =23.1$ cm/s) consists of periodic generation of pairs of three-dimensional solitary waves (lumps) in a V-shaped pattern downstream of the source. In the reference frame of the laboratory, these unsteady lumps propagate in a direction oblique to the motion of the source and are damped by viscosity. In the current study, the interaction of lumps generated by two equal strength pressure sources moving side by side in parallel straight lines is investigated experimentally via photography-based techniques. The first lump generated by each source, collides with the lump from the other source in the center-plane of the two sources. It is observed that a steep depression is formed during the collision. Soon after the collision, this depression radiates energy in the form of small-amplitude radial waves. After the radiation, a quasi-stable pattern is formed with several rows of localized depressions that are qualitatively similar to lumps but exhibit periodic oscillations in depth, similar to a ``breather". The shape of the wave pattern and the period of oscillations depend strongly on the distance between the soures. [Preview Abstract] |
Tuesday, November 22, 2016 1:56PM - 2:09PM |
R14.00003: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R14.00004: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R14.00005: An experimental study of wave coupling in gravity surface wave turbulence Quentin Aubourg, Joel Sommeria, Samuel Viboud, Nicolas Mordant Weak turbulence is a theoretical framework aimed at describing wave turbulence (in the weakly nonlinear limit) i.e. a statistical state involving a large number of nonlinearly coupled waves. For gravity waves at the surface of water, it provides a phenomenology that may describe the formation of the spectrum of the ocean surface. Analytical predictions of the spectra are made based on the fact that energy transfer occurs through 4-wave coupling. By using an advanced stereoscopic imaging technique, we measure in time the deformation of the water surface. We obtain a state of wave turbulence by using two small wedge wavemakers in a 13-m diameter wavetank. We then use high order correlator (bi- and tri-coherence) in order to get evidence of the active wave coupling present in our system as used successfully for gravity-capillary wave turbulence [1]. At odds with the weak turbulence theory we observe 3-wave interaction involving 2 quasi linear wave and a bound wave whose frequency lies on the first harmonics of the linear dispersion relation. We do not observe 4-wave coupling within the accuracy of our measurement. \newline [1] Aubourg {\&} Mordant, Phys. Rev. Fluids 1, 2016 [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R14.00006: Numerical simulation of the capillary-gravity waves excited by an obstacle Hideshi Hanazaki, Ryosuke Inomata Capillary gravity waves excited by an obstacle are investigated by the unsteady numerical solution of the Euler equations. It is well known that the large-amplitude upstream advancing solitary waves are generated periodically under the resonant condition of \textit{Fr}$=$1 (\textit{Fr}: Froude number), i.e., when the phase velocity of the long surface waves agrees with the mean flow speed. With capillary effects (\textit{Bo}\textgreater 0), short waves are newly generated by the upstream solitary waves of large amplitude. In this study it is investigated how the characteristics of the solitary waves and the short waves, especially their amplitudes, change due to the variation of the obstacle height and the Froude number. The results will be compared also with the solutions of the forced KdV-type equations. [Preview Abstract] |
Tuesday, November 22, 2016 2:48PM - 3:01PM |
R14.00007: Kinematic criterion for breaking of shoaling waves Dan Liberzon, Uri Itay Validity of a kinematic criterion for breaking of shoaling waves was examined experimentally. Results obtained by simultaneous measurements of water surface velocity by PTV and of the propagation velocity of a steep crest up to the point of breaking inception during shoaling will be reported. The experiments performed in a large wave tank examining breaking behavior of gentle spillers during shoaling on three different slopes suggest a validity of the recently proposed kinematic criterion. The breaking inception was found to occur when the horizontal velocity of the water surface on the steep (local steepness of 0.41-0.6) crest reaches a threshold value of 0.85-0.95 of that of the crest propagation. The exact moment and position of breaking inception detected using a Phase Time Method (PTM), characterizing a unique shape of the local frequency fluctuations at the inception. Future implementation of the PTM method for detection of breaking events in irregular wave fields will be discussed. [Preview Abstract] |
Tuesday, November 22, 2016 3:01PM - 3:14PM |
R14.00008: The generation of symmetric and asymmetric lump solitons by a bottom topography Zhiming Lu A group of Lump solutions to the (2+1)-dimensional Kadomtsev-Petviashvili (KP) equation is obtained analytically by making use of Hirota bilinear transform method. Then the generation of symmetric and asymmetric lump solitons by an obliquely-placed three-dimensional bottom topography is numerically investigated using the forced Kadomtsev-Petviashvili-I (fKP-I) equation. The numerical method is based on the third order Runge-Kutta method and the Crank-Nicolson scheme. The main result is the asymmetric generation of asymmetric lump-type solitons downstream of the obstacle.The lump soliton with a smaller amplitude is generated with a longer period and moves in a larger angle with respect to the positive x-axis than the one with a larger amplitude. The amplitude of the lump solitons strongly depend on the volume of the obstacle rather than the shape. Finally the effects of the detuning parameter on the generation of lump solitons is also studied. [Preview Abstract] |
Tuesday, November 22, 2016 3:14PM - 3:27PM |
R14.00009: Identifying features of Kelvin ship wakes via spectrogram analysis Scott McCue, Ravindra Pethiyagoda, Timothy Moroney A method for observing and measuring ship wakes is to employ an echo sounder to record the surface elevation over time as a ship passes nearby. The resulting output signal corresponds to the cross-section of the ship wake taken in the direction of travel. The surface elevation at the echo sounder can be visualised as a spectrogram through the use of many short-time discrete Fourier transforms. In this study, we identify and explain features of spectrograms of ship wakes, concentrating on the differing effects that linearity and nonlinearity have on the wave time-frequency signal. These results have the potential to contribute to practical scenarios in which spectrograms are used to calculate the energy contained within a given ship wake and the effect that the propagating wake wash will have when it interacts with the coastal zone. [Preview Abstract] |
Tuesday, November 22, 2016 3:27PM - 3:40PM |
R14.00010: Random coupling of acoustic-gravity waves in the atmosphere Christophe MILLET, Francois LOTT, Christophe HAYNES In numerical modeling of long-range acoustic propagation in the atmosphere, the effect of gravity waves on low-frequency acoustic waves is often ignored. As the sound speed far exceeds the gravity wave phase speed, these two types of waves present different spatial scales and their linear coupling is weak. It is possible, however, to obtain relatively strong couplings via sound speed profile changes with altitude. In the present study, this scenario is analyzed for realistic gravity wave fields and the incident acoustic wave is modeled as a narrow-banded acoustic pulse. The gravity waves are represented as a random field using a stochastic multiwave parameterization of non-orographic gravity waves. The parameterization provides independent monochromatic gravity waves, and the gravity wave field is obtained as the linear superposition of the waves produced. When the random terms are retained, a more generalized wave equation is obtained that both qualitatively and quantitatively agrees with the observations of several highly dispersed stratospheric wavetrains. Here, we show that the cumulative effect of gravity wave breakings makes the sensitivity of ground-based acoustic signals large, in that small changes in the parameterization can create or destroy an acoustic wavetrain. [Preview Abstract] |
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